Conventional cranes of this kind usually have the sheave shafts of their upper and lower block assemblies arranged parallel to the boom pivot axis so that the sheave blocks can follow the pivotal movement of the boom (luffing action LA) without restriction. This is represented in FIG. 1a of the drawings. Normally, the allowable movement of the lower block assembly laterally (side lead angle SL) is relatively small, less than 5.degree., to be within the allowable fleet angle on the sheaves. This is represented in FIG. 1b of the drawings. In some cases, however, it may be required to have a greater side lead angle, such as when manipulating a load using two hoisting devices, as illustrated in FIG. 1c of the drawings. The conventional solution is to suspend the upper block assembly from the boom using a universal joint (UJ), as is shown in FIGS. 1d and 1e of the drawings. However, even with this arrangement, the side lead angle is still limited due to the fact that the lead-in sheaves (LIS) on the boom must also swivel and there are normally restrictions on the angel of adjustment which the lead-in sheaves can achieve.